Aliphatic carboxylic acids such as succinic acid and adipic acid are being extensively used as starting materials for synthesizing foods, medicines, and other chemical products. These aliphatic carboxylic acids have conventionally been produced industrially from petroleum-derived starting materials. In recent years, however, various aliphatic carboxylic acids can be produced from a wide range of biological starting materials by a fermentation operation using microorganisms while attaining a high carbon yield. For example, succinic acid, adipic acid, and the like can be produced by fermentation.
The starting materials to be used in the production of aliphatic carboxylic acids through fermentation generally are saccharides such as glucose, grape sugar, and cellulose. However, there are cases where polysaccharides are contained as impurities and where the saccharides used as starting materials are not completely assimilated by the microorganisms and partly remain to come into the aliphatic carboxylic acids. Furthermore, although it is widely known that ammonia is used as a neutralizer in microbial fermentation, amino acids also generate as by-products in this case.
In the case where ammonia is used as a neutralizer, the aliphatic carboxylic acids in the fermentation broth are present in the form of ammonium salts. For recovering the aliphatic carboxylic acids, it is necessary to subject the carboxylic acid salts to salt interchange with an acid. When sulfuric acid is used as the acid, the ammonium salt of sulfuric acid generates as a by-product together with the aliphatic carboxylic acids.
There are many reports on methods for recovering such aliphatic carboxylic acids. Meanwhile, there are almost no report on a method for recovering the by-product ammonium salt of sulfuric acid, although this ammonium salt contains by-products of the fermentation in a large amount and is useful as a fertilizer.
A crystallization method is a general method for recovering the ammonium salt of sulfuric acid from an aqueous solution containing the ammonium salt of sulfuric acid. Usually, this method frequently involves recycling of the crystallization mother liquid in order to obtain a sufficiently high recovery percentage of the ammonium salt of sulfuric acid.